Organic dyes are known, which are diketopyrrolopyrroles (DPPs) of formula (I), which are employed as pigments, used in the production of durable paints and varnishes.
Daniel T. Gryko et al. Organic Letters 14 (2012) 2670 disclose a synthetic approach to π-expanded diketopyrrolopyrroles. A three-step strategy appears to be very general and starts with the preparation of diketopyrrolopyrroles followed by N-alkylation with bromoacetaldehyde diethyl acetal and electrophilic aromatic substitution. The final reaction regioselectively furnishes fluorescent dyes.
WO2013/092474 relates to compounds of formula (III):
where Ar denotes a homo- or heteroaromatic system.
Daniel T. Gryko et al. Chemical Communications 49 (2013) 8368 (DOI: 10.1039/c3cc44728f) report the synthesis of π-expanded diketopyrrolopyrroles. The new functional dyes possess enhanced properties when compared with expanded DPPs in terms of fluorescence quantum yield. By placing two amine groups at peripheral positions of the resulting dyes, values of 2PA (two-photon absorption) cross-section on the level of 2000 GM were achieved, which in combination with high φfl, generated a two-photon brightness of ˜1000 units at 840-970 nm.
There is still a need for stable water-insoluble organic pigments, which might find application in the dyeing industry. In addition, the development of fluorometric techniques and the extensive use thereof in modern biomedical techniques and diagnostics (e.g. optical imaging) means there is steady growth in demand for new compounds with improved fluorescence properties in the visible range. Provision of compounds with high fluorescence quantum yield is required.